Because of their wide availability, relative inexpense, and versatility, polyurethane elastomers with specific physical properties have been adapted for use in a diverse array of technical applications. One such application is as conductive and semi-conductive members in image forming devices. It has been desirable to develop more compact image forming devices having a smaller device footprint. Consequently, the need for development of reduced-geometry printer components arose. However, it has been discovered that the necessary size adaptations altered the functioning of various elastomeric components with respect to, for example, required compressive forces, nip widths, resiliency, triboelectric charging capacity, and rotational torque. Utilization of reduced-geometry components having the same elastomeric properties as the originally-sized components often results in the occurrence of unacceptable print variations and distortions in the final printed product. Hence, new materials adapted to confer physical properties which compensate for the reduced geometry and restore the quality of the final printed product are needed. In particular, such materials are needed with respect to the roll components of electrophotographic printers.
The polyurethane elastomers may be formed via one-shot or prepolymer methods. Utilizing a prepolymer synthesis route, the polyurethane is formed by sufficiently curing a urethane mixture typically comprising a polyurethane prepolymer, and one or more curatives (typically chain-extenders and/or cross-linkers), as well as various solvents, catalysts, and other additives depending on the need. Curatives must comprise at least di-functionality to act as chain extenders, and tri-functionality to act as cross-linkers or to promote networking within the matrix, functional groups being generally defined as groups comprising active hydrogens, for example, amines or hydroxyls.
Reaching a desired elastomer hardness by manipulating selection of the urethane prepolymer and curative components of the final elastomer often results in unacceptable compromises in other properties of the elastomer. Typically, plasticizers are used to reduce the hardness of polymeric elastomers such as cast polyurethanes. However, plasticizing additives are not chemically bound into the polymer matrix and are therefore free to migrate throughout, including to the surface of a roll formed therefrom, resulting in unacceptable print variations in electrophotographic print applications. Hence, there is clearly a need for soft polyurethane elastomers that also maintain a suitably low compression set, and for methods of manufacturing them. In addition, it would be advantageous to provide inexpensive, more versatile graft polymer curatives which could confer desirable property profiles to polyurethane elastomers required by particular applications.